The induction heating of metal products to desired temperatures is well-known and commonly practiced. In conventional induction heating, a metal workpiece is heated by an induction heating coil by placing the coil around the workpiece and passing electric current through the coil. The electric current passing through the coil produces a magnetic field and induces secondary currents in the workpiece. The secondary currents flowing through the workpiece heat it.
It is sometimes desirable to heat different areas or zones of the workpiece so as to obtain a non-uniform temperature profile along the length of the workpiece. By applying different amounts of power to different zones of a workpiece placed within the induction coil, reproducible temperature profiles can be obtained. These reproducible temperature profiles yield desirable effects in the workpiece, especially in metallurgical processes involving crystal growth.
In accordance with the present invention, a desired temperature profile is obtained by shunting various zones of the induction heating coil, corresponding to various zones of a workpiece, with a saturable reactor. For a particular combination of voltage and current through a zone of the heating coil, the saturable reactor may be made to conduct and divert current from the zone of the heating coil. By controlling the amount of current diverted, or shunted, across a zone, the power in that zone, and therefore the temperature of the workpiece in that zone, may be controlled.
It is an object of the present invention to individually control the amount of power to one or more of several zones of an induction heating coil to produce a desired temperature profile in a workpiece.